Comorbidity among anxiety and depressive disorders has been well documented, yet the etiological pathways contributing to this comorbidity are not clearly understood. Most of the research regarding the genetic and environmental sources of comorbidity among these disorders has been conducted using adult samples and suggests that genetic and nonshared environmental sources of covariation are important. Relatively little is known about the behavioral genetic aspects of comorbidity among anxiety and depressive disorders in children and adolescents. In an effort to extend the current knowledge regarding the comorbidity of internalizing disorders to younger populations, the proposed research will employ data from a large population-based sample of female twins to explore the comorbidity among Separation Anxiety Disorder (SAD), Depression (DEP) and Generalized Anxiety Disorder (GAD) and parse the sources of comorbidity into latent genetic and environmental factors using multivariate genetic analyses. In addition, the proposed research seeks to further clarify the nature of comorbidity of SAD with DEP and GAD by including measured personality (introversion and neuroticism) and environmental characteristics (socioeconomic disadvantage and paternal absence) in multivariate genetic analyses. Advances have been made in the study of comorbidity as well as personality and environmental characteristics as risk factors for internalizing disorders among youth; yet, these areas of study remain largely independent of one another. The proposed project seeks to integrate these areas of investigation. [unreadable] [unreadable]